1. Field of the Invention
The present invention relates generally to a lithographic projection apparatus and more particularly to a lithographic projection apparatus including beam directing components.
2. Background of the Related Art
The term xe2x80x9cpatterning structurexe2x80x9d as here employed should be broadly interpreted as referring to means that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term xe2x80x9clight valvexe2x80x9d can also be used in this context. Generally, the said pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning structure include:
A mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support structure will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
A programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using suitable electronic means. More information on such mirror arrays can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference. In the case of a programmable mirror array, the said support structure may be embodied as a frame or table, for example, which may be fixed or movable as required.
A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. As above, the support structure in this case maybe embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table; however, the general principles discussed in such instances should be seen in the broader context of the patterning structure as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning structure may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatusxe2x80x94commonly referred to as a step-and-scan apparatusxe2x80x94each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally  less than 1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a scanning apparatus, one or more dies maybe provided in a single scan. Alternatively, each die may be made up of a plurality of stripes, each printed in a single scan, which are stitched or butted together.
In a manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemomechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4, incorporated herein by reference.
For the sake of simplicity, the projection system may hereinafter be referred to as the xe2x80x9clensxe2x80x9d; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a xe2x80x9clensxe2x80x9d. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such xe2x80x9cmultiple stagexe2x80x9d devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference.
According to an embodiment of the present invention there is provided a lithographic projection apparatus comprising:
a radiation system for providing a projection beam of radiation;
a support structure for supporting patterning structure, the patterning structure serving to pattern the projection beam according to a desired pattern;
a substrate table for holding a substrate;
a projection system for projecting the patterned beam onto a target portion of the substrate in a scanning motion; characterized in that
at least one of said radiation system and said projection system comprises a sliding electron-optical element for generating an electromagnetic field for acting on said projection beam such that the optical axis of said electromagnetic field is displaced in at least one direction perpendicular to said axis in synchronism with said scanning motion.
Because the electron-optical element scans with the projection beam, the electron-optical element need only generate fields over the volume traversed by the projection beam at a given moment, rather than over the whole volume traversed during a scanning motion. The fields can therefore be generated more accurately and several beamlets can be passed simultaneously. Further advantages of the invention are described in the following text.
According to a second embodiment of the invention there is provided a lithographic projection apparatus for imaging a mask pattern in a mask onto a substrate, the apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of charged particles;
a first object table provided with a first object holder constructed to hold a mask;
a second object table provided with a second object holder constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; characterized by:
means for generating a magnetic field in the vicinity of the source of said charged particle beam to impart an angular velocity component to off-axis charged particles emitted from said source.
According to a third embodiment of the invention there is provided a lithographic projection apparatus for imaging a mask pattern in a mask onto a substrate, the apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of charged particles;
a first object table provided with a first object holder constructed to hold a mask;
a second object table provided with a second object holder constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; characterized in that
said projection system comprises at least four quadrupole lenses.
According to a fourth embodiment of the present invention, there is provided a lithographic projection apparatus for imaging a mask pattern in a mask onto a substrate, the apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of charged particles;
a first object table provided with a first object holder constructed to hold a mask;
a second object table provided with a second object holder constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; characterized in that:
said projection system comprises a magnetic field generator for generating a magnetic field in the vicinity of the mask, of the substrate and of the beam path from mask to substrate, said magnetic field being substantially parallel to said beam path and increasing in strength from said mask to said substrate.
According to a fifth embodiment of the invention there is provided a lithographic projection apparatus for imaging a mask pattern in a mask onto a substrate, the apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of charged particles;
a first object table provided with a first object holder constructed to hold a mask;
a second object table provided with a second object holder constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; characterized in that:
said projection system comprises at least two electromagnets, wherein the electromagnets nearest the mask and substrate have no pole pieces adjacent the mask and substrate respectively.
According to a sixth embodiment of the present invention there is provided a lithographic projection apparatus for imaging a mask pattern in a mask onto a substrate, the apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of charged particles;
a first object table provided with a first object holder constructed to hold a mask;
a second object table provided with a second object holder constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; characterized in that:
said projection system has a length of less than about 350 mm, preferably less than about 320 mm.
According to a seventh embodiment of the present invention there is provided a lithographic projection apparatus for imaging a mask pattern in a mask onto a substrate, the apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of charged particles;
a first object table provided with a first object holder constructed to hold a mask;
a second object table provided with a second object holder constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; characterized in that
said projection system comprises an electromagnetic system functioning as imaging lenses and an electrostatic system for varying the beam energy in the projection system.